1. Field of the Invention
The present invention relates to an anti-static hard coat film that is used in a display, such as a liquid crystal display (hereafter “LCD”) apparatus, and is both anti-static and resistant to scratch. The invention also relates to a method of manufacturing the same. In particular, the present invention relates to an optimal anti-static hard coat film for an In-Plane Switching (hereafter “IPS”) LCD apparatus, and to a method of manufacturing the same.
2. Related Art
A conventional display, such as a CRT (Cathode Ray Tube) or a LCD apparatus, is provided with a hard coat film 80 in which a hard coat layer 82 with superior resistance to scratch is formed on top of a base film 84 as shown in FIG. 6A.
However, with such a hard coat film, the surface resistance of the hard coat layer itself is normally high at 1×1013 Ω·cm or above, so that a problem occurs in that it is easy for electrically charged dust and the like in the periphery to electrically adhere to the surface of the hard coat layer.
To reduce the surface resistivity of the hard coat layer in view of the above, as shown in FIG. 6B, an anti-static hard coat film 87 is formed by adding a preset amount of anti-static particles 86, such as antimony tin oxide (hereafter “ATO”) or an aqueous polymer into a hard coat layer 88 provided on top of a base film 84 has been disclosed.
With the above anti-static hard coat film, however, the hard coat layer is relatively thick, so that in order to achieve a preset anti-static effect, large amounts of anti-static particles or aqueous polymer have to be added. As a result, a number of problems were observed for such a hard coat film, such as a significant reduction in a total light transmission and deterioration in the effectiveness of the film as a hard coat.
JP 11-42729 A discloses an anti-static hard coat film 89 formed, as shown in FIG. 6C, with an anti-static layer 88, which includes anti-static particles 86, or an anti-static layer composed of a thin metal film between a base film 84 and a hard coat layer 82.
However, since the anti-static layer is located below the relatively thick hard coat layer and so is at some distance from the surface, the value of the surface resistance is still high, making it difficult to achieve a preset anti-static effect.
Also, with the disclosed anti-static hard coat film, the anti-static layer is sandwiched between the hard coat layer and the base film, both of which are electrical insulators. This has made it difficult to earth the anti-static layer.
For the above reasons, an anti-static hard coat film with the following laminated structure has been proposed. A hard coat layer and an anti-static layer are successively formed on a base film so that the anti-static layer is present at the surface. That is to say, the formation of an anti-static layer of an ionizing radiation-curable resin that is irradiated with ionizing radiation on the hard coat film has been proposed.
However, the thickness of the anti-static layer is normally a few microns or less, so that if this layer is simply irradiated with ionizing radiation, curing defects occur due to impedance by oxygen, which is present in the air in the periphery. As a result, it has been difficult to form an anti-static layer with a preset surface resistivity and resistance to scratch.
On the other hand, a different method of manufacturing an anti-static hard coat film is disclosed by JP 8-112866 A. According to this method, as shown by FIG. 7, a UV curable resin 92 is applied onto a base member 93, with this then being laminated with an anti-static layer 91 that has been formed in advance on backing liner 94. After this, the UV curable resin 92 is cured by irradiating, via the anti-static layer 91, the UV curable resin 92 with UV rays 96, either after the backing liner 94 has been peeled off the anti-static layer 91 side or alternatively with the backing liner 94 still in place. As shown in FIG. 7, this process can be carried out with the assistance of rolls 95.
However, even when backing liner has been used, it has not been easy to evenly laminate the anti-static layer and the applied UV curable resin with even thicknesses and without creases. As one example, it was observed that when the anti-static layer is a thin film with a thickness of 5 μm or below or when the anti-static layer has a width of 10 cm or above, the laminar pressure of the anti-static layer and the applied UV curable resin becomes uneven, making it effectively impossible to laminate the resin and the anti-static layer.
It has also been observed that when UV curable resin is exposed to light to cure the resin, the resin contracts significantly as it cures, which makes it even more difficult to laminate the anti-static layer and the hard coat-layer composed of the UV curable resin. Accordingly, even if the anti-static layer and the applied UV curable resin are aligned before the resin is cured, it has not been easy to laminate the layer and the resin at preset positions once the resin has cured.
There has been a further problem with the disclosed method in that since the anti-static layer is formed by being cured in advance, it is difficult to cause reactions at the interface between the anti-static layer and the hard coat layer. Consequently, there is a reduction in the adhesion of the anti-static layer and the hard coat layer, which has led to various problems being observed, such as the anti-static layer peeling off or a preset resistance to scratch not being achieved.
Also, with the disclosed method, the anti-static layer needs to be produced using a separate process, which has disadvantages such as an increase in the number of manufacturing processes, an increase in the manufacturing time, and the need to use backing liner.